The present invention relates to aircraft lighting and, more particularly, to a sealed beam high intensity discharge lamp system for an aircraft.
High intensity discharge (HID) lamps offer significant advantages over other lamps conventionally used in aircraft applications, such as quartz halogen or incandescent sealed beam lamps used as utility/cargo baylights, wing and engine scan lights, logo lights, landing lights and taxi lights. When compared with quartz halogen lamps, HID lamps provide (i) nearly twice the photometric performance at less than half the energy consumption, (ii) extended lamp life by a factor of about four, (iii) better shock resistance and (iv) less heat generation.
U.S. Pat. No. 4,345,178 describes a high intensity reflector lamp intended for use in a commercial aircraft for landings at night. The lamp comprises an arc discharge tube mounted cross axially within a parabolic reflector. The parabolic reflector is sealed to a cover glass with the body of arc tube located at about the focus of the parabolic reflector. To minimize the possibility of high voltage arc-over, the envelope formed by the reflector and cover glass is filled with nitrogen at about one atmosphere of pressure.
While the aforesaid patent forecasts the use of a high intensity reflector lamp in commercial aircraft, no explanation is given to how this may be successfully accomplished. In fact, most if not all commercial aircraft today use quartz halogen or incandescent sealed beam lamps as utility/cargo bay lights, wing and engine scan lights, logo lights, landing lights and taxi lights. As an exception, low power (50 Watts or less) HID lamps are today manufactured for use in aircraft, but these lamps do not use a sealed beam.
The present invention provides a system for enabling successful use of HID lamps in aircraft, including in particular high power lamps for use as landing lights and taxi lights. To this end, the invention utilizes a sealed beam HID lamp which during normal operation has an external temperature considerably lower than the external temperature of a quartz halogen or incandescent sealed beam lamp of equivalent light output. This enables the HID lamp to be located in areas that are susceptible to potentially explosive fuel vapor concentrations without the need for explosion proof containment structure, with resultant benefits in weight and cost reduction. The lower external temperature also permits increased usage of advanced composite materials in-aircraft structure that cannot be used with conventional landing and taxi lights. In particular, some structural composite materials such as fiber reinforced epoxies or polyimides are susceptible to thermal damage at temperatures above 120xc2x0 C.-180xc2x0 C. Conventional landing and taxi lights operate at temperature that may damage these composites.
The lower external temperature arises in part from the use of a gas fill in the sealed beam. Among other things the gas fill provides for convective cooling of the lamp especially at high altitudes, and provides a constant internal pressure which prevents internal arcing from internal electrodes to any surrounding conductors such as the reflective surface of the reflector which may be conductive. According to the invention, a detector is provided to monitor the seal integrity of the sealed beam HID lamp, particularly a hermetically sealed lamp, and further to provide a response to seal failure resulting in disablement of the lamp. Exemplary means for accomplishing seal failure detection include radioactive detection, pressure monitoring, and chemical sensing, or other means wherein detection of a failed seal is followed by an electrical output used to inhibit lamp operation, as by terminating or precluding lamp operation.
Thus, according to the present invention, a high intensity discharge lamp system comprises a sealed beam HID lamp, lamp power control circuitry, and a seal integrity sensing device which monitors the seal integrity of the lamp and inhibits lamp operation upon detection of a loss of seal integrity.
In an embodiment, the sealed beam HID lamp includes an enclosure filled with a gas including radioactive elements, and the seal integrity sensing device includes a radiation sensor for sensing radiation emitted by the radioactive elements.
In another embodiment, the sealed beam HID lamp includes an enclosure filled with a gas, and the seal integrity sensing device includes a pressure transducer for sensing the pressure of the gas.
In a further embodiment, the sealed beam HID lamp includes an enclosure filled with a gas, and the seal integrity sensing device includes a sensor for sensing at least one component of the gas.
The present invention also provides a high intensity discharge lamp system comprising a shroud, a HID lamp ignitor housed within the shroud, and a sealed beam HID lamp removably mounted to the lamp ignitor within the shroud.
In one embodiment, the lamp has connecting pins protruding from the rear thereof, and the ignitor has receptacles for receiving the connecting pins. The connecting pins are surrounded by a rubber boot.
In an embodiment, the lamp ignitor is connected by a cable to a ballast separate from the shroud.
The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention, such being indicative, however, of but one or a few of the various ways in which the principles of the invention may be employed.